The present invention relates generally to liquid crystal displays and more particularly to an improved liquid crystal display exhibiting enhanced optical viewing performance.
Liquid crystal displays, which were first introduced in the 1970's and have since been used in watches, clocks, pocket calculators, portable personal computers, navigational instruments and the like, are electronically switched displays that make use of changes in the reflective properties of liquid crystals present in an electric field. A typical liquid crystal display comprises a liquid crystal display panel (also commonly referred to as a liquid crystal display cell), said panel comprising a thin film of liquid crystals sandwiched between a pair of transparent substrates, each of the transparent substrates typically having a transparent electrically conductive coating applied to the liquid crystal side thereof, said transparent coating functioning as an electrode. The liquid crystal display panel is typically positioned between a pair of glass (or other transparent) cover plates, the cover plates being sealed together around their respective edges. The cover plates may be assembled with spacers between them to maintain a constant separation distance. Two crossed axis polarizers are positioned between the cover plates, one polarizer being adhered to the front of the liquid crystal display panel and the other polarizer being adhered to the rear of the liquid crystal display panel. When a voltage is applied selectively across the electrodes, the liquid crystal molecules between them are rearranged or switched in polarization so that light is either reflected or absorbed in the region bounded by the electrodes to form characters or graphics. Many liquid crystal displays include a backlight for night or dark viewing, and many liquid crystal displays include a layer of indium tin oxide or another suitable material positioned between the front polarizer and the front cover plate for use as an electromagnetic interference shield. Some liquid crystal displays intended for use in cold environments also include a layer of indium tin oxide or another suitable material positioned between the rear polarizer and the rear cover plate and electrically connected to a power source for use as a heating element.
Some of the advantages of liquid crystal displays, as compared to other digital displays, are their comparatively low voltage and power requirements. Unfortunately, however, one of the principal disadvantages of liquid crystal displays is that, due to their low contrast and a “washed-out” effect caused by back-reflected ambient light seen by a viewer, they cannot easily be read under high ambient light conditions, such as when placed in direct sunlight.
One approach which has been taken to improve the viewing performance of liquid crystal displays, particularly when viewed under high ambient light conditions, has been to apply an anti-reflection coating to the front of the front cover plate. Although such an approach has provided some improvement to the viewing characteristics of liquid crystal displays by reducing the amount of back-reflected light seen by the viewer, further improvement is greatly needed.
A few patents in the field of liquid crystal display technology are described below.
In U.S. Pat. No. 5,818,559, inventor Yoshida, which issued Oct. 6, 1998, there is disclosed a liquid crystal display having different linear expansion coefficients among the materials of the display. More specifically, the liquid crystal display comprises a liquid crystal cell and a polarizing sheet stuck with an adhesive layer, said cell comprising a liquid crystal interposed between a pair of resinous substrates, at least one of which has a transparent electrode, and said polarizing sheet comprising a polarizing film interposed between a pair of resinous protective films, wherein difference in a linear expansion coefficient between the resin of the substrate facing the polarizing sheet and the resin of the protective film facing the liquid crystal cell is less than 0.50×10−5/° C.
In U.S. Pat. No. 5,523,873, inventors Bradford, III et al., which issued Jun. 4, 1996, and which is incorporated herein by reference, there is disclosed a liquid crystal display comprising first and second polarizers sandwiching a liquid crystal layer therebetween, electrode means for applying a voltage across the liquid crystal layer, and a heater disposed adjacent (directly or otherwise) the first polarizer, the heater comprising a conductive layer having a substantially planar flex circuit buss bar disposed thereon, the buss bar for delivering power to the conductive layer, thereby enabling the conductive layer to heat the liquid crystal display.
In U.S. Pat. No. 3,869,196, inventor Kubota, which issued Mar. 4, 1975, and which is incorporated herein by reference, there is disclosed a liquid crystal display device wherein the thickness and the loss of light by reflection are said to be decreased by using one surface from each of a polarizer and an analyzer for forming a cell in which the liquid crystal material is confined.
Other patents of interest include U.S. Pat. No. 5,179,457, inventors Hirataka et al., which issued Jan. 12, 1993; U.S. Pat. No. 5,430,607, inventor Smith, issued Jul. 4, 1995; U.S. Pat. No. 5,570,214, inventors Abileah et al., which issued Oct. 29, 1996; U.S. Pat. No. 5,594,568, inventors Abileah et al., which issued Jan. 14, 1997; U.S. Pat. No. 5,706,068, inventors Abileah et al., which issued Jan. 6, 1998; and U.S. Pat. No. 5,739,881, inventors Xu et al., which issued Apr. 14, 1998, all of which are incorporated by reference.